Review of some significant claimed irregularities in Scandinavian postglacial uplift on timescales of tens to thousands of years – earthquakes in Denmark?

Abstract

Abstract. The postglacial uplift and surrounding subsidence in Scandinavia is well described as close to regular, and the phenomenon is similar on timescales of tens, hundreds and thousands of years studied via geodesy, seismology and geology. Searches for irregularities in the form of earthquakes claimed in the scientific literature have disclosed many earthquakes right after the Ice Age, 9000 yr ago, and some later cases for further evaluation. In a previous report, the present authors have mentioned doubts about the validity of some of the most significant claimed irregularities. In the present paper, a review is made of these significant claimed irregularities in the south-western flank of the Scandinavian postglacial uplift and subsidence via literature studies of geodetic and geological claims of earthquakes as well as discussions in the field. Geodetic observations exist for all of Scandinavia that describe the phenomenon on a scale of 10s-100s of years. Earthquake observations in seismology are of relevance in the same timescales. Geological studies of dated shore lines describe the postglacial vertical earth-surface motion in a quite different timescale of 100s-1000s of years. There is a need for integration of these observations geographically. This is happening in the various timescales in the DynaQlim project. The review finds the claims unlikely to be earthquakes concerning the following: (1) geodynamical motion in the Copenhagen area, (2) a palaeo-earthquake in Laesø and (3) the recently proposed water level discrepancy in the southern part of Denmark. The assessment is less certain, but falls to improbable when concerning (4) proposed palaeo-earthquakes by Hallandsåsen in south-western Sweden.

An M > 6 Earthquake ~750 BC in SE Sweden

“…Because the instrumental seismic records do not exceed M 4.3 (for example the Dec. 16, 2008 event with epicenter 60 km west of the horst area here discussed), the seismological community has great difficulties in accepting any earthquake in the Late Holocene reaching M6 or above e.g. [21]. Coincidence in time between different events occurring at different sites or outcrops in nature is, for a geologist, a strong indication of a mutual driving force, whilst it, for a seismologist, might be just a matter of statistical coincidence.…”

“…Coincidence in time between different events occurring at different sites or outcrops in nature is, for a geologist, a strong indication of a mutual driving force, whilst it, for a seismologist, might be just a matter of statistical coincidence. It is quite interesting that Gregersen and Voss [21] concluded: "one is left with a choice in the evaluation between coincidences or common cause: earthquake. The field trip convinced the participating seismologists that the claimed signs of earthquakes must be seriously taken into account".…”